1. Field of the Invention
This invention relates generally to the separation and recovery of metals from concentrates and other metal containing materials and, in particular, to a process using a ferric fluoborate solution to leach concentrates and solubilize the metals and then to extract at least some of the metals particularly impurity metals using organic extractants, ion exchange resins and the like to form metal containing raffinate solutions from which metals can be recovered by electrowinning or other recovery processes. The fluoborate metal containing raffinate solution contains fluoboric acid produced in the extraction step which acid is controlled by converting the acid to a metal fluoborate before the recovery step.
2. Description of Related Art
The separation of metals from their ores or other materials such as sludges, concentrates, residues, waste products, baghouse dusts and the like is well known. Over the years, for example, lead has been produced from ores such as galena by thermal means such as roasting followed by smelting and refining. Roasting or sintering processes require environmental controls because of emissions such as SO.sub.2 if the feed to the process is a sulfide ore. Because of these problems hydrometallurgical processes have been developed which are typically environmentally preferred.
A hydrometallurgical process for producing electrolytic lead from galena concentrate is shown in U.S. Pat. No. 5,039,337 to M. Olper and P. Fracchia, which patent is hereby incorporated by reference. In this process galena concentrate is leached with an aqueous solution of ferric fluoborate and fluoboric acid with ferrous fluoborate, lead fluoborate and elemental sulfur being formed according to the reaction: EQU 2Fe (BF.sub.4).sub.3 +PbS.fwdarw.2Fe(BF.sub.4).sub.2 +Pb(BF.sub.4).sub.2 +S
The solid residue composed of elemental sulfur and gangue is separated and the solution of ferrous fluoborate and lead fluoborate is sent to a diaphragm electrolytic cell wherein pure lead is deposited at the cathode and at the anode ferrous ion is oxidized to ferric ion. The solution of ferric fluoborate regenerated at the anode is recycled to the leaching step.
The above ferric fluoborate process may also be used to leach other "impure" lead sources such as lead bullion, lead smelter speiss and matte and secondary lead materials such as from batteries. Similarly, for these processes, the lead source is leached to form a lead fluoborate and ferrous fluoborate solution which is then electrolyzed in a diaphragm electrolytic cell.
While the ferric fluoborate leaching process is a preferred method in the lead industry, impurities and/or byproducts in the leach solution adversely impact the process and are preferably removed and recovered before the electrolysis step of the process. Impurities such as antimony, bismuth and tin present in the concentrate when leached are particularly troublesome and, if not removed from the leach solution, will result in an "impure" lead product being formed at the cathode and cause other processing problems.
Other ores and metal containing materials are also desirably treated to separate and recover their metal values by hydrometallurgical processes. For example, the mineral tetrahedrite having the general formula (Cu,Fe).sub.12 Sb.sub.4 S.sub.13 is typically concentrated to form a material containing a mixture of copper and antimony sulfides with ancillary silver and having the general formula Cu.sub.2 S. Sb.sub.2 S.sub.3 (+Ag.sub.2 S). Other sulfide copper ores include bornite, chalcopyrite, chalcocite and covellite. Similarly, zinc concentrates, typically containing lead and/or copper sulfides and like materials, are also desirably treated by hydrometallurgical processes to separate and recover their metal values.
Copper bearing materials for hydrometallurgical recovery processes include copper sulfide concentrates with varying amounts of iron and impurities such as antimony, arsenic and bismuth, white metal, copper matte and blister, scrap and anodes. Processing of the copper bearing material generally comprises leaching the material, removing the impurities and/or byproducts from the leach solution and electrowinning the leach solution to recover the copper.
A ferric fluoborate leach solution has been found to be useful to treat the above and other metal containing materials to separate and recover the metals. In the ferric fluoborate leach process and in other leach processes, metal containing solutions are formed which may be electrowon or otherwise processed, e.g., by precipitation, to form commercial metal products. This usually requires that the fluoborate leach solution be treated to separate unwanted metals or impurities from the leach solution by using extractants such as organic extractants, ion exchange resins and the like (hereinafter generally referred to as extractants). The organic extractants are essentially water immiscible and form an extract phase and raffinate phase. The metal to be recovered may also be recovered by extracting (separation) from the fluoborate leach solution.
These extractants are typically "hydrogen based" in that, when used, the removal of metals or impurities from the leach solution is accompanied by the generation of fluoboric acid in the extracted leach solution commonly termed raffinate. The fluoboric acid in the raffinate does not contribute to regeneration of ferric fluoborate needed for recycling. The ferric fluoborate concentration will decrease to zero unless the fluoborate ions (which are transferred from bonding with metal ions to hydrogen ions in the extraction process) are eventually returned to bonding with iron ions. Since the process requires the repeated use of regenerated ferric fluoborate, it is necessary to control the formation of fluoboric acid in the system. For example, in U.S. Pat. No. 5,039,337 to Olper et al., supra, if it is necessary to remove impurities such as antimony and tin from the leach solution before electrowinning, the overall effectiveness of the process will be compromised by the formation of fluoboric acid in the raffinate in the impurity extraction step.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method for the control of the concentration of fluoboric acid in a raffinate solution formed in the ferric fluoborate treatment of metal containing materials when an extractant is used to selectively remove a metal or impurity metal from the leach solution.
It is another object of the present invention to provide a method for the hydrometallurgical treatment of metal containing materials such as lead, zinc, and copper metal containing materials, and mixtures thereof, using a ferric fluoborate solution as a leachant whereby the concentration of fluoboric acid generated during the process in a raffinate solution is controlled so that the solution can be effectively electrowon forming a ferric fluoborate containing solution for recycling and the leaching of additional metal containing material.
Other objects and advantages of the present invention will be readily apparent from the following description.